This handgun was created from resin with 3-D printer technology. / Department of Justice

by Susan Davis, , USA TODAY

by Susan Davis, , USA TODAY

WASHINGTON - A long-standing federal law banning guns that can go undetected by metal detectors and X-ray machines is set to expire next week, and it is not clear Congress can agree on how to extend the measure.

It is the only piece of legislation affecting guns that will be taken up by both chambers this year despite a congressional session that began in January with sweeping calls for an overhaul of the nation's gun laws in the wake of the Sandy Hook Elementary School shooting.

The House of Representatives is likely to vote Tuesday on a simple, 10-year extension of the Undetectable Firearms Act, first enacted during the Reagan administration in 1988 and reauthorized without issue under Presidents Clinton and George W. Bush.

The law bans the manufacture, possession and sale of firearms that can go undetected by metal detectors and requires handguns be manufactured in the shape of a gun so they can be seen on X-ray machines.

Senate Democrats want to amend the law to mandate that metal has to be a permanent part of the gun, closing what they call a loophole that allows removable metal parts. Republicans support a clean authorization, but there is opposition to changing existing law from conservative lawmakers and gun rights groups such as Gun Owners of America.

Sen. Charles Schumer, D-N.Y., plans to offer an extension of the law with the provision included. Supporters say it will address concerns about 3-D printing technology, which can produce solid objects out of digital models and did not exist commercially when the law was first enacted.

"The House bill is better than nothing, but it's not good enough," Schumer said Monday in a statement calling for support of the Senate provision.

The Senate returns Dec. 9 - the same day the law expires, raising the prospects that it will sunset and Congress will need to fix it retroactively.

Sen. Charles Grassley, R-Iowa, said that congressional Republicans support renewing the law, but that Democrats have "knowingly mischaracterized this debate." Grassley said Democrats sparked GOP frustrations when they tried to quietly move a one-year renewal before the Thanksgiving break. Republicans objected, but Grassley said the law "will be extended without delay" if Democrats agree to a long-term, simple renewal.

The National Rifle Association, the nation's most influential gun lobby, does not oppose the law but has not weighed in publicly on the additional provision sought by Democrats.

Attorney General Eric Holder called on Congress last month to renew it, citing threats posed to law enforcement officials and security screenings in airports and government buildings, among other public safety concerns.

"Whatever people's feelings are about gun safety legislation, this is something we should all agree needs to be reauthorized - and even expanded," he said.

The law's renewal highlights the sensitive nature of the debate over even long-established gun laws in the current political climate.

The Senate tried and failed in April to advance legislation to expand background checks in response to Sandy Hook, but the Democrats could not overcome a Republican filibuster and the bill has been stalled since. The House never took it up.

No other gun legislation has advanced this year or is likely to next year.